**4. Removal of ARGs and ARB by WWTPs**

The effluent of WWTPs is an important source of pollution to the nation's water resources, and 3.5 million Americans annually are getting sick after touching water they thought was safe [52]. WWTPs are hotspots for emerging contaminants namely antibiotics, heavy metals, ARGs, and HMRGs [32]. Research on the related topic has shown the proliferation of ARGs [8], the occurrence of antibiotics and ARGs and their influence on the receiving river [53], and distribution of antibiotic resistance in the effluents of WWTPs [32]. In order to limit the occurrence and spread of antibiotic resistance, treatment methods should be able to destroy ARGs in addition to inactivating pathogens [54].

*Anaerobic, anoxic, and aerobic reactors* were studied to treat wastewaters contaminated by high concentrations of various ARGs [9]. Aerobic and anaerobic treatment processes are low energy and environmentally friendly strategies which are mostly used to treat chemical oxygen demand (COD); moreover, they can successfully remove ARB and ARGs [55].

The aerobic treatment happens in the presence of air and microorganisms which utilize oxygen to change over organic contaminants to carbon dioxide, water, and biomass (aerobes). The anaerobic treatment forms occur in the absence of air and anaerobes microorganisms which do not require air to change over organic contaminants to methane and carbon dioxide gas and biomass [51].

Another low energy treatment alternative is anaerobic-aerobic sequence (AAS) bioreactor that reduce carbon amount as a pretreatment in an anaerobic condition and after that perform aerobic treatment [55]. Metagenomics investigations of this treatment technique demonstrated the impact of this approach on antibiotic resistance and ARGs. AAS expelled over 85% of ARGs in the influent wastewater which implies it was more proficient than aerobic and anaerobic units (83 and 62%, respectively) [55].

In another study, Munir et al. [56] investigated the occurrence and distribution of ARGs including *sul*(1), *tet*(W), and *tet*(O) and their associated bacteria in the effluent of five WWTPs to assess the efficiency of different processes. ARGs and ARB removal ranged 2.37-log to 4.56-log in activated sludge, oxidative ditch and rotatory biological contactors and 2.57-log to 7.06-log in MBR [56].

As mentioned before, WWTPs are known as sources of antibiotic resistance. Auerbach et al. [14] studied two activated sludge wastewater treatment plants and two freshwater lakes for the presence of 10 tetracycline resistance genes. Qualitative PCR and quantitative PCR methods were used to detect tetracycline resistance genes and quantify the number of tetracycline resistance gene copies per volume of sample, respectively. Their results showed that both WWTPs contain more diverse types of tetracycline resistant genes than the background natural lake water samples. They revealed that the WWTPs are a source of ARGs dissemination. *tetQ* and *tetG* in the treatment processes were attenuated, however, the UV disinfection did

Presence of specific genes encoding resistance to tetracyclines (*tetQ* [48]*, tetA* [49], and *tetO* [50]), sulfonamide (*sul*1 [49] *sul*2 [50]), erythromycin (*mphB* [49]), quinolone (*qnrD* [49] and *qnrS* [50]), beta-lactams (*cepA, cfxA* [48]*, blaCTX-M,* and *blaTEM* [50]), erythromycin (*ermB*), methicillin (*mecA*), vancomycin (*vanA)* [50], and aminoglycoside (*aac(3)-II, aacA4, aadA, aadB, aadE, aphA1, aphA2, strA* and *strB* [51]) were analyzed and confirmed by recent studies. The results of these studies prove that WWTPs are the main source of antibiotic resistance transmission.

The effluent of WWTPs is an important source of pollution to the nation's water resources, and 3.5 million Americans annually are getting sick after touching water they thought was safe [52]. WWTPs are hotspots for emerging contaminants namely antibiotics, heavy metals, ARGs, and HMRGs [32]. Research on the related topic has shown the proliferation of ARGs [8], the occurrence of antibiotics and ARGs and their influence on the receiving river [53], and distribution of antibiotic resistance in the effluents of WWTPs [32]. In order to limit the occurrence and spread of antibiotic resistance, treatment methods should be able to destroy ARGs

*Anaerobic, anoxic, and aerobic reactors* were studied to treat wastewaters contaminated by high concentrations of various ARGs [9]. Aerobic and anaerobic treatment processes are low energy and environmentally friendly strategies which are mostly used to treat chemical oxy-

The aerobic treatment happens in the presence of air and microorganisms which utilize oxygen to change over organic contaminants to carbon dioxide, water, and biomass (aerobes). The anaerobic treatment forms occur in the absence of air and anaerobes microorganisms which do not require air to change over organic contaminants to methane and carbon dioxide

Another low energy treatment alternative is anaerobic-aerobic sequence (AAS) bioreactor that reduce carbon amount as a pretreatment in an anaerobic condition and after that perform aerobic treatment [55]. Metagenomics investigations of this treatment technique demonstrated the impact of this approach on antibiotic resistance and ARGs. AAS expelled over 85% of ARGs in the influent wastewater which implies it was more proficient than aerobic and

gen demand (COD); moreover, they can successfully remove ARB and ARGs [55].

not reduce the ARGs [14].

84 Antimicrobial Resistance - A Global Threat

**4. Removal of ARGs and ARB by WWTPs**

in addition to inactivating pathogens [54].

anaerobic units (83 and 62%, respectively) [55].

gas and biomass [51].

Removal of antibiotics including sulfamethazine, sulfamethoxazole, trimethoprim, and lincomycin had been studied in five different WWTPs using aerobic/anaerobic treatment methods [57]. The results of this study showed the range of −11.2% to 69.0% efficiency for different pharmaceutical compounds including sulfamethazine, sulfamethoxazole, trimethoprim, and lincomycin. The negative removal efficiency belonged to lincomycin and because of its high load in wastewater [57].

To sum it up, aerobic reactors alone are not very effective and biological treatment methods can remove antibiotics, ARB, and ARGs successfully if anaerobic and aerobic reactors operate in sequence. Despite the fact that anaerobic treatment is energy efficient and has high performance, aerobic treatment is more common in municipal WWTPs. Anaerobic treatments are often used to treat wastewater that contains high loads of organic matter like industrial wastewater and needs warm temperature (35°C). Activated sludge, which is an aerobic treatment, is studied in this project and the results will help to advance the efficiency of activated sludge bioreactors in treatment plants.

Some studies aimed to remove ARGs in raw domestic wastewater by *constructed wetlands* with different flow configurations or plant species [58]. In addition, disinfection methods including chlorination, ultraviolet (UV) irradiation and sequential UV/chlorination treatment on the inactivation of ARGs have been studied [54, 59, 60]. Recently, nanomaterials with antimicrobial activity have been offered as a novel defense against ARGs [61]. Moreover, the removal of ARGs from treated wastewater in the coagulation process was examined [62]. In one of the recent works, the effect of biochar amendment on soil ARGs was assessed and the outcomes showed that biochar is pretty operational [63].

Many diverse combinations of *nanomaterial* have proved that antimicrobial nanotechnology can be effective defenses against drug-resistant organisms, ARB, and ARGs. Two different mechanisms are probable when nanoparticles treat antibiotic resistance; the first mechanism is called Trojan Horse that develops drug-delivery characteristics. In this system, a functionalized nanomaterial is joined with antibiotics and nanomaterial enters inside cells and afterward discharge significant amounts of toxic ions [57]. In the second system, a mix of antibiotic and nanomaterials result in synergistic impacts, that means they battle ARGs independently [61]. Meanwhile, removal efficiency and mechanism of four ARGs including *tetA*, *sul2*, *ermB*, and *ampC* have been found using graphene oxide nanosheet. The removal efficiency was reported in the range of 2.88 to 3.11 logs at 300 µg/mL nanosheet solution showing the potential of graphene oxide nanosheet as an innovative and effective adsorbent for treatment of ARGs [64].

The potential for antimicrobial nanomaterials to restrict the propagation of multi-drug resistant pathogens while avoiding the generation of new nanomaterial-resistant organisms was studied by a group of researchers led by Aruguete [61]. They prepared a combination of nanomaterials functionalized with molecular antibiotics. This combination consisted of liposomes, dendrimers, and an antibiotic that is inside of a polymer nanoparticles capsules, and inorganic nanoparticles with antibiotic molecules attached to the surfaces [61]. In this study, silver nanoparticles coated with a water-soluble polymer called polyvinylpyrrolidone were used to combat nanomaterial-resistant organisms [61]. This experiment proved that nanomaterial combinations are able to perform like an antibiotic and to be toxic to *Pseudomonas aeruginosa* bacteria which was resistant to multiple drugs [61]. The results of this study are in line with the previous reports on the silver-based polymers used as antimicrobial biomaterials for water treatment [65, 66].

**Acknowledgements**

**Conflict of interest**

**Author details**

**References**

Fateme Barancheshme and Mariya Munir\*

Charlotte, Charlotte, NC, United States

\*Address all correspondence to: mmunir@uncc.edu

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The authors acknowledge funding support from the Department of Civil and Environmental

Development of Antibiotic Resistance in Wastewater Treatment Plants

http://dx.doi.org/10.5772/intechopen.81538

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The authors declare that the research was conducted in the absence of any commercial or

financial relationships that could be construed as a potential conflict of interest.

Department of Civil and Environmental Engineering, University of North Carolina at

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[2] Pal C et al. Metal resistance and its association with antibiotic resistance. In: Advances in

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Engineering, the University of North Carolina at Charlotte.

Nanomaterials have been considered as a defense against multiple drug resistance because of their antimicrobial activity [59, 61, 62, 67]. Antibacterial activities of nanoparticles depend on two fundamental elements, physicochemical properties of nanoparticles and type of target bacteria. Regardless of the fact that there is a correlation in a couple of aspects of the antibacterial activity of nanoparticles, singular investigations are challenging to generalize since most of the researchers perform experiments using accessible nanoparticles and bacteria, rather than targeting particular and preferred nanoparticles or bacteria [68]. Nanoparticles which are utilized in lab-scale studies are not well-known and correlating them with physicochemical properties for full-scale production is not reliable.

A mix of nanomaterials and molecular antibiotics draws in much consideration recently, since they are effective in killing multi-drug resistant isolates of pathogenic bacterial species and combating an expansive range of ARB and ARGs [56, 69].

Nanomaterials play controversial roles in regard to antibiotic resistance; on one hand, as mentioned before, they have been considered as a defense against multiple drug resistance because of their antimicrobial activity, and on the other hand, they can encourage the development of antibiotic resistance in the environment [56, 70]. Overall, more information is needed concerning the mechanisms behind the antimicrobial activity of nanomaterials and their potential for influencing the development of resistance in environmental systems.
